A study for a M2M communication service that supports inter-device data communication in the case where a human interaction does not exist or is extremely limited is in progress.
The M2M communication service is in the spotlight in an aspect of reducing costs for managing a device via automated control and communication, and is recognized as a technology that is applicable to fleet management of a vehicle and products mounted on a vehicle, smart metering, home automation, health care, etc.
Unlike a terminal of a general communication system, a M2M communication system that supports M2M communication should consider a case of supporting a device transmitting/receiving limited data during only a limited time.
For example, a device that performs smart metering just transfers a metered numerical value to a smart metering server only one time per month, and a device that performs health care just updates health care information from a health care server only one time per day.
A server of a M2M communication system may transfer the same data to a plurality of devices that have subscribed to the same service, may receive data from the plurality of devices that have subscribed to the same service, and may instruct the devices to remain in an idle mode for a time for which data transmission/reception does not occur.
Therefore, a device that remains in an idle mode performs a system access procedure in order to make a transition to a connected state from the idle mode at a point where data transmission/reception to/from the server is required.
In the case where a plurality of devices belonging, to a specific group perform the system access procedure in order to receive data from a server, or transmit data to the server, it may be difficult for the plurality of devices to succeed in accessing the system at a time.
A device that has failed in accessing the system should perform an access back-off for a predetermined time and retry a system access.
Therefore, a data transmission/reception delay with a device belonging to the group occurs by a time of the access back-off.